Think I posted a question a couple of years ago surrounding plugs and received little to no feedback. So I went on this journey almost alone.

I swapped out from engine builder recommended NGK BR8EIX to 10’s when I upped the boost and leaned off the mid range fuelling circa 2yrs ago. From memory they are closer to non projected tip image. I noticed the egt’s a touch cooler and less prone to triggering the knock sensor over 1bar. I pulled them back out last April during the spring service after a year or so being allowed to do their job uniterupted. The tip colour was spot on with no fouling or carbon build up.

If the car is mostly street driven it will be other demands than for a track day car.

I use ngk b8 egv, many people use it for racing, and tuned turbo cars. I use them successfully in bikes aswell. They are supposed to be very sturdy, and give a really good spark. Which you really notice in the startability of the single cylinder bikes. They seem tolerant to low speed street driving aswell.

I heard that the surface gap plugs fouls very easily, amd need a really hefty ignition system, especially on a turbo car. Nothing for my car, but might be possible to get some benefits if you build a good ign.system and use the car for track only._________________´80 924 Turbo

Forgot about those for a moment.. They are Gold Palladium Plugs but I think they might be discontinued?
They sure want a lot of money for them on ebay but I found that a local parts store shows them "in stock" for $6 each, it says..

I think I ruled them out because they aren't resister plugs..
Well, I don't have a (functioning) radio on the 931, nor do I plan to add one, but do have an MS box, so I'm not sure about non-resistor plugs..
You don't experience any problems with non-resistor plugs Cedric?
I guess I could try them and see what happens..

I had no idea that Mittelmotor used surface gap plugs!! I thought that was a crazy idea of mine..
They look like they would be pretty easy to clean up if they foul out..

Do you have any idea which surface gap plugs Mittelmotor used?
A problem with them is you cannot change the gap, and you need a small gap to not "blow out' the spark with high boost.. Because dense air is harder to throw an arc through if I understand correctly.. Maybe Mittelmotor uses different ones with a closer gap, don't know..

Have you ever tried 9's?
Surick told me that he is running plugs with a heat range equivalent to a Bosh 3, which is a NGK 9.. But also says he idles at 14.7 to keep them from fouling, good idle, but I'm having trouble getting a smooth idle that lean..

Here is a heat range chart for Xref..

I don't know exactly what plugs he is running but Bosch 3 = NGK 9 and he is running what? 20-22psi ish iirc..

It seems a lot of tuners swear by standard br8es plugs but their is a tuning channel on youtube I have been watching to try to learn how to tune, and he swears by 4554 plugs which are the R5671A-8 4554 V-Power RACING plugs.. And I'm seeing him tuning 1000HP 2.0ish Hondas so that's pretty serious boost in the high 30's.. https://www.youtube.com/watch?v=k4b1peZwaP0
It's a bit Honda ricey but pretty entertaining and he actually shows what he is doing on his laptop tuning at times, hard to find..

Carrera RSR wrote:

I swapped out from engine builder recommended NGK BR8EIX to 10’s when I upped the boost and leaned off the mid range fuelling circa 2yrs ago.

10s!?
You have been running 10s for 2 years and haven't fouled them out in your street driven car? Wow..
What is your IAT and EGT on boost?
Maybe I should try 9s or 10s since you have such good luck that cold..
They say run the coldest plug you can keep from fouling out.._________________80 Turbo - Slightly Modified

Last edited by Fasteddie313 on Mon Jul 02, 2018 4:46 am; edited 1 time in total

Have no issues running without resistors. However those eix plugs seems similar and maybe more easy to get hold on. With our engines(not that tuned) its probably not super sensitive, if you buy a quality plug and at a good heat range._________________´80 924 Turbo

I jumped from 8's to 10 thinking, if i had bought the 9's and they didn't foul, I'd wish I had gone for 10's. If the 10 fouled, then I knew I could back pedal to the 9. The 10 worked, so I'll stay there for now

In a nutshell, my specs are
IAT's usually 6-8deg higher than ambient air.
EGT's usually 850deg pushing into 900's on a long boost
Idle and cruise bob on 14.7's
WOT at 10.1
Mid range AFR on WOT/full boost at high 11's to low 12's until the boost switch opens up the WUR's fuelling at 4800rpm
Usually 1.1-1.2bar boost which feels like the sweet spot of power and boost noise/theatre of fun. Probably overspinning it though!
Forged pistons to take a little battering from boost, temps and the occasional det occurrence_________________1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252

I use NGK BPR8ES plugs and everything is working just fine. Just avoid rich mixtures at low load and idle to avoid fouling em.
Keep in mind that if you run EFI with some kind of VR crank sensor, than non-resistive plugs can interfere with it and jam or spoil it's readings_________________WBR, Shurick
'79 931 -- intercooled K26-3060-6.10 turbo @ 1.2 bar, EFI+EDIS, 951S brakes, stripped interior, 951 look.
'86 924S -- R.I.P.